The present invention relates to an improvement in heat exchanger design, more particularly to thin film distillation systems.
It is well known in the art to provide a distiller which utilizes the condensation of vapor on one side of a heat conductive plate to provide the heat for evaporation of a liquid on the opposite surface of the plate. In some systems it can often be important to minimize the overall temperature difference through which the process occurs. One method which allows the process to occur without requiring a high temperature differential is to maintain a thin film of liquid on the evaporative side and a minimum film of condensate on the condensing side. This enables the thermal resistance of the films to be minimized.
Currently used methods include application of liquid with a squeegee such as in U.S. Pat. No. 5,409,576 to Tleimat or liquid application by spraying the film on a rotating disc and allowing condensate removal by centrifugal acceleration such as in U.S. Pat. No. 4,731,159 to Porter et al. Others use gravity as in U.S. Pat. Nos. 4,329,204 and 4,402,793 both to Petrek et al. Though each apparatus has its advantages, each require extensive hardware and fairly large spacing between plates. What is needed is a system which allows the use of compact simple hardware particularly suited to smaller systems.
Until the present invention, compact low energy requirement evaporative systems were not practical and thus have not been commercialized. The purpose of this invention is to enable the efficient application of a thin film of liquid to closely spaced heat exchanger surfaces without having to resort to expensive and precise mechanisms. Additionally, an apparatus meeting these requirements should also enable the removal of condensate from closely spaced surfaces without the need to rely upon rotation of the heat exchanger or to require specific orientation of the surface to enable removal of the condensate by gravity.
A new and non-obvious distillation system which accomplishes these requirements is introduced herein. In its most simplistic form, the invention comprises a pad of resilient material which can hold and move a distilland liquid to be applied by capillary action, and a means to move the pad repeatedly across an evaporator heat transfer surface to apply and renew a thin film of liquid on the surface. The pad is connected to a supply of the liquid, which is continually fed to the surface as it evaporates. In practice the pad is sized to move easily in the gap between two closely spaced corrugations of a surface thus applying liquid to each side of the gap.
In a preferred embodiment the heat transfer surface is a corrugated cylinder or bellows comprising a thin heat conductive material. A set of pads is aligned to rotate about the axis of the heat exchanger within the outer corrugations forming the heat transfer surface. These pads apply a liquid to be evaporated. Another set of pads, aligned to rotate about the center of the heat exchanger within the inner corrugation serve to remove condensate. This embodiment could be utilized as the heat transfer system of a vapor compression distiller where vapor leaving the outer surface is compressed and introduced to the inside surface which is otherwise sealed from the outside in order to maintain the required pressure differential.
As such it is an object of the present invention to provide a thin film heat exchanger system which places a thin film of liquid for evaporation on a surface by use of a capillary applicator.
Another object of the present invention is to provide a heat exchanger utilizing a capillary applicator capable of applying a thin film of liquid between two closely spaced surfaces.
Still a further object of the present invention is to provide a liquid distiller which operates efficiently and requires minimum energy input into the system to perform.